Remove POSTLINKER_SUPPORTS_ASMTYPE configuration variable
---------------------------------------------------------

In the "expgen" stage, Raptor invokes elf2e32 to generate an assembly file. The
assembly file is then compiled and linked into the target component.

Originally this only worked for RVCT, because the assembly file was written in
RVCT's syntax. The Symbian Foundation wanted it to work for GCCE as well, so a new
option, --asm=gas|armas, was added to elf2e32. When invoked with --asm=gas, GNU
assembly syntax is used. When invoked with --asm=armas, RVCT assembly syntax is
used. The latter is also the default.

Since this was a new option, Raptor couldn't assume that it was always available.
Unless the configuration variable POSTLINKER_SUPPORTS_ASMTYPE was set, Raptor would
*not* invoke elf2e32 with the --asm option.

It was up to the user (or the people responsible for the content in
epoc32/sbs_config) to set the variable, presumably by creating a new variant. See
https://bugreports.qt.nokia.com/browse/QTSDK-759 for an example of when people got
into trouble with this.

Let "new" be a version of elf2e32 that supports the --asm option and "old" a version
that doesn't. Then we have the following fault cases for different combinations of
compiler and elf2e32 version:

    COMPILER | ELF2E32 | FAULT CASE
    ---------+---------+-----------
      RVCT   |   OLD   | --asm used
      RVCT   |   NEW   | None
      GCCE   |   OLD   | Fails whether --asm is used or not
      GCCE   |   NEW   | --asm not used

We got rid of the first fault case by not using --asm for RVCT at all. Hence
POSTLINKER_SUPPORTS_ASMTYPE wasn't needed anymore for RVCT.

We got rid of the last fault case by always using --asm for GCCE. That leaves the
combination GCCE + old elf2e32, but that is a problem that doesn't have a solution.
Hence POSTLINKER_SUPPORTS_ASMTYPE wasn't really useful for GCCE either and could be
removed.

